Do Do Do, DoDo Do-Do, DoDoDo-Doo DoDoDo DoDoo...
Does that (hopefully somewhat correct) tune ring any bells? Here's a reminder:
Once upon a time there were two Italian plumbers named Mario and Luigi. Mario and his sidekick resided in the Mushroom Kingdom, a monarchy ruled by the beautiful Princess Peach. Mario's mission: stop the villain Bowser from his numerous attempts to kidnap the lovely princess.
There you have it. One little video game and decades of fan madness (not to mention worldwide notoriety) have ensued. Here's one example (among many) of awesome Mario fan art.
(Post-it image unrelated to animation. Credit)